Zimbabwe's High Court has rejected an appeal by state lawyers against its decision to free MDC party official Roy Bennett on bail.

But he will not be immediately released as prosecutors lodged a fresh appeal, his lawyer Beatrice Mtetwa said.

Bennett, who was set to become a junior minister in a unity government agreed between President Robert Mugabe and MDC leader and Prime Minister Morgan Tsvangirai, was arrested on February 13 and charged with plotting terrorism.

He could face to life in jail if convicted.

The arrest of Bennett and the detention of several opposition activists is an early test for Zimbabwe's new unity government, which many hope will ease the country's economic crisis.

Mr Tsvangirai has been pushing for the release of Bennett and activists from his MDC party.

"The judge has dismissed the prosecution's application for leave to appeal against the bail decision," Ms Mtetwa said.

"In the normal course, Roy ought to be released, but we know that the Attorney-General's office has in the past disregarded court rulings and they could appeal to the Supreme Court."

Prosecutor Chris Mutangadura said Bennett would remain in custody until the Supreme Court heard the prosecution's appeal.

"We have to exhaust all options available to us. If the Supreme Court also dismisses our application, then that is the end of the road," he said.

Zimbabwean authorities this week released more than a dozen detainees, including prominent human rights campaigner Jestina Mukoko, who had been held for about three months.